Climate change

Climate change transformed the world from the final days of civilization into something almost unrecognizable.


Over deep time, the great ecological challenge for life on earth lay in the fact that the sun continues to grow hotter throughout its life. Life on earth collectively developed an extremely effective means of countering this trend by absorbing carbon from the atmosphere into its own bodies, and burying that carbon in the ground with each death. Over time, this trend worked so well that it even produced ice ages like the Pleistocene in which humans first evolved, while those bodies transformed deep inside the earth into coal, petroleum, and natural gas.

#The Anthropocene

See Anthropocene

#Early Anthropocene

The Holocene began just like any of the Pleistocene's other interglacial periods, but this time it created the perfect conditions for the beginnings of agriculture, leading to the rise of civilization. As the practice of agriculture spread, forests cleared to make way for more fields began the Anthropocene. At first, human agricultural activity succeeded primarily in extending the Holocene by countervailing natural trends towards returning to the colder conditions that generally prevailed in the Pleistocene (and sometimes even slipping, as in the “Little Ice Age” between 1650 and 1850).

#High Anthropocene

Following the “Little Ice Age,” though, an industrial revolution led to the extraction and burning of coal, petroleum, and natural gas as fossil fuels. Civilizations effectively took half of the carbon that life had sequestered over the preceding 100 million years and released it into the atmosphere over the course of two centuries.

Ultimately, though, even this proved insufficient to transform the earth on its own — but it did prove enough to trigger other feedback loops. With the highest concentrations of carbon in the atmosphere seen in 3 million years, the earth began to grow warm enough to thaw permafrost and heat deep ocean waters, which released huge reserves of methane, an even more potent greenhouse gas than carbon dioxide. Melting ice reduced the albedo effect, one means by which the earth cools itself, by having large areas covered in white snow and ice that reflect light and heat back out into space. As white snow and ice melted to reveal much darker land and water beneath it, these darker colors absorbed more heat, causing even more snow and ice to melt.

A combination of self-interest and disbelief fueled a public rejection of scientists’ predictions, even as new positive feedback loops forced scientist to make ever more extreme predictions which failed to keep pace with how quickly the earth kept changing. Of course, no system as complex as the earth would ever warm in a simple or predictable way. Raising temperatures in some areas meant that lakes would not freeze over in winter, which meant heavier snow in many areas. Melting ice water weakened and eventually shut down the Gulf Stream that had previously heated much of Europe, plunging it into a century of bitter cold. Non-intuitive consequences of a warming world such as these stymied collective effort to reduce or mitigate climate change.


Climate change contributed greatly to the collapse of the global civilization that had set it in motion, but continued throughout the Rusting Age. Eventually, after several centuries of climatic chaos, the climate reached a new equilibrium, thanks to the formation of a new cloud regime. This new regime covered much of the planet in clouds much of the time, creating a strong albedo effect that reflects enough heat back into space, high enough in the atmosphere to limit the continued greenhouse effect.

#The new normal

The Fifth World resembles conditions previously seen in the Paleocone-Eocene Thermal Maximum (PETM), the last time that earth’s atmosphere had similar levels of carbon. Originally, when scientists discovered fossils of palm trees and alligators living near the Arctic Circle during the PETM, they inferred that such conditions must have left much of the world uninhabitable. Later, though, they found fossils of very similar creatures from close to the equator, revealing that when the greenhouse effect becomes that strong, nothing else matters — not latitude and not seasonality. In the Fifth World, the poles differ from the equator by only a few degrees. Likewise, the hottest summer day and the coldest winter night differ by only a few degrees. The world has become a largely single-biome planet, with jungles found from pole to pole, covering every continent, including Antarctica.

#Oceanic changes

The ice caps have melted, raising sea levels around the world by 216 feet. This has significantly changed the world’s coastlines, including the complete submergence of Bangladesh and Florida, the formation of the Amazonian Sea in South America, the Golden Gulf in North America, and the Tethys Sea in Eurasia, and the reshaping of the British Archipelago.

Runaway climate change also caused marked acidification across the world’s oceans. Though not acidic enough to burn a human’s skin, it proved devastating to fish generally and shellfish in particular. Cephalopods, on the other hand, prospered, and took advantage of the empty niches left behind by mass extinction in the world’s oceans to become the most common form of life encountered there. Some varieties of octopus have become longer-lived, allowing their marked intelligence the time they need to flourish, leading to the emergence of octopus cities and cultures in the deep. Rather than “fishing,” coastal communities in the Fifth World go “squidding,” expecting to catch squid and octopus rather than less common fish.

#Weather conditions

Across most of the Fifth World, overcast conditions prevail perhaps 300 days out of the year, or about 85% of the time. It rains quite frequently, though the thick jungle canopies often serve as quite effective umbrellas. The trees also help greatly to reduce the burden of humidity and mugginess through evapotranspiration. In fact, without the forests that Fifth World communities actively manage, many areas may well have become uninhabitable, as the combination of heat and humidity would raise “wet bulb temperatures” to levels that would make human survival untenable.

Large storms have become more frequent, and the storms have become larger. The largest storms have stretched as far as a quarter of the planet’s diameter. The strongest storms have reached wind speeds of 200 miles per hour. The Atlantic hurricane season and the Pacific typhoon season both now last from April until January. The Atlantic season averages about 5 major hurricanes per year.

And yet, people in the Fifth World deal with these storms without much interruption. Buildings made of simple materials might collapse in a storm, but when they do they do not threaten injury, and people can rebuild them easily afterwards. Some communities build homes on stilts or in trees to avoid flooding. Others find shelter in caves or other underground shelters. Ways of life that make one vulnerable to powerful storms have simply become untenable in this new world. For the people who remain, powerful storms constitute just another fact of life.


Temperatures change very little from summer to winter, but changes in day length remain unchanged. Near the poles, many plants have begun adapting to the strange conditions. In these areas where the climate has changed most drastically, empty niches have provided strong pressures selecting for those varieties that can take the best advantage of several months of uninterrupted light, and then do the best job of preserving food over the following months of uninterrupted darkness.

Across most of the planet, the Coriolis effect creates wet and dry seasons (these provide relative terms; the “dry season” still usually involves more humidity and rainfall than the area saw in centuries past).

#Effects on plants and animals

The rapid pace of climate change posed an existential threat to much of the plant kingdom, as they had little hope of moving quickly enough to keep up with it on their own. Fortunately, humans took an active part in moving plants much further than they could on their own, bringing plants from tropical areas into new bioregions as the climate changed. With that threat addressed, plants could benefit from the increased carbon dioxide in the atmosphere to proliferate widely. So much plant growth has resulted in increased oxygen levels in the atmosphere as well.

A warming planet generally pushed animals towards smaller body sizes, in keeping with Bergmann’s rule. This includes humans, which have become markedly smaller than their ancient ancestors. On the other hand, the increased oxygen in the atmosphere has caused insects to grow much larger, including dragonflies the size of gulls. Between these two effects, humans in the Fifth World do, on rare occasions, encounter insects as large as half their own size, and sometimes even larger.

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